I do sometimes doubt some of the techniques used by SOME so called behaviorists! And would suspect by your post that the methods used somewhat have varied in their approach!

I am far far away from helping you with this problem, but wonder it there a 'very placid' dog that you know of that you could start to maybe walk with - with both dogs kept on their leads intially?

I ask this because a dog training class I used to attend had a great dane that had been attacked as a puppy! The trainer asked if I would spend some time with my dog ( one which was bombproof and not in the least bit interested in other dogs) I spent a couple of lessons just walking past this dog with my dog - initially the Dane was going nuts! but with time and patience it did begin to relax and the owner was able to walk it past me without any major outbursts! I am unable to say whether this was sucessful long term as the Dane owner did not continue coming to the classes!

Don't know if this is of any help! but just an idea! my theory being if you can install confidence in your dog with just one other dog it may give you foundations to build on.

All the best!

Maybe someone else can come up with something more positive
regards
DT